Semiconductor processing method of promoting photoresist adhesion to an outer substrate layer predominately comprising silicon nitride

ABSTRACT

A semiconductor processing method of promoting adhesion of photoresist to an outer substrate layer predominately comprising silicon nitride includes, a) providing a substrate; b) providing an outer layer of Si 3 N 4  outwardly of the substrate, the outer Si 3 N 4  layer having an outer surface; c) covering the outer Si 3 N 4  surface with a discrete photoresist adhesion layer; and d) depositing a layer of photoresist over the outer Si 3 N 4  surface having the intermediate discrete adhesion layer thereover, the photoresist adhering to the Si 3 N 4  layer with a greater degree of adhesion than would otherwise occur if the intermediate discrete adhesion layer were not present. Further, a method in accordance with the invention includes, i) providing an outer layer of Si 3 N 4  outwardly of the substrate, the outer Si 3 N 4  layer having an outer surface; ii) transforming the outer Si 3 N 4  surface into a material effective to promote adhesion of photoresist to the Si 3 N 4  layer; and iii) depositing a layer of photoresist over the transformed outer Si 3 N 4  surface, the photoresist adhering to the Si 3 N 4  layer with a greater degree of adhesion than would otherwise occur if the outer Si 3 N 4  surface were not transformed.

RELATED PATENT DATA

This patent resulted from a continuation application of U.S. patent application Ser. No. 08/567,090 now U.S. Pat. No. 5,926,739, which was filed on Dec. 4, 1995.

TECHNICAL FIELD

This invention relates generally to semiconductor processing methods of promoting adhesion of photoresist to an outer substrate layer predominantly comprising silicon nitride.

BACKGROUND OF THE INVENTION

Microcircuit fabrication involves provision of precisely controlled quantities of impurities into small regions of a silicon substrate, and subsequently interconnecting these regions to create components and integrated circuits. The patterns that define such regions are typically created by a photolithographic process. Such processing sets the horizontal dimensions on the various parts of the devices and circuits. Photolithography is a multistep pattern transfer process similar to stenciling or photography. In photolithograpy, the required pattern is first formed in reticles or photomasks and transferred into the surface layer(s) of the wafer through photomasking steps.

Inherent in photolithograpy is application and adherence of photoresist materials to underlying substrates. The resist must be capable of adhering to these surfaces through all the resist processing and etch steps. Poor adhesion brings about severe undercutting, loss of resolution, or possibly the complete loss of the pattern. Wet etching techniques demand a high level of adhesion of the resist film to the underlying substrates.

Various techniques are used to increase the adhesion between resist and a substrate such as, a) dehydration baking prior to coating; b) use of hexamethyldisilazane (HMDS) and vapor priming systems to promote resist adhesion for polysilicon, metal. and SiO₂ layers, and c) elevated temperature post-bake cycles. HMDS functions as an effective adhesion promoter for silicon and silicon oxide containing films, but provides effectively no surface-linking adhesion promotion with respect to silicon nitride films.

Accordingly, it would be desirable to develop alternate and improved techniques for providing better adhesion of photoresist to silicon nitride films.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below with reference to the following accompanying drawings.

FIG. 1 is a diagrammatic sectional view of a semiconductor wafer fragment at one processing step in accordance with the invention.

FIG. 2 is a view of the FIG. 1 wafer fragment at a processing step subsequent to that shown by FIG. 1.

FIG. 3 is a view of the FIG. 1 wafer fragment at a processing step subsequent to that shown by FIG. 2.

FIG. 4 is a view of the FIG. 1 wafer fragment at a processing step subsequent to that shown by FIG. 3.

FIG. 5 is a diagrammatic sectional view of an alternate embodiment semiconductor wafer fragment at one alternate processing step in accordance with the invention.

FIG. 6 is a view of the FIG. 5 wafer fragment at a processing step subsequent to that shown by FIG. 5.

FIG. 7 is a diagrammatic sectional view of yet another alternate embodiment semiconductor wafer fragment at yet another alternate processing step in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts”(Article 1, Section 8).

In accordance with one aspect of the invention, a semiconductor processing method of promoting adhesion of photoresist to an outer substrate layer predominately comprising silicon nitride comprises the following steps:

providing a substrate;

providing an outer layer of Si₃N₄ outwardly of the substrate, the outer Si₃N₄ layer having an outer surface;

covering the outer Si₃N₄ surface with a discrete photoresist adhesion layer; and

depositing a layer of photoresist over the outer Si₃N₄ surface having the intermediate discrete adhesion layer thereover, the photoresist adhering to the Si₃N₄ layer with a greater degree of adhesion than would otherwise occur if the intermediate discrete adhesion layer were not present.

In accordance with another aspect, a semiconductor processing method of promoting adhesion of photoresist to an outer substrate layer predominately comprising silicon nitride comprises the following steps:

providing a substrate;

providing an outer layer of Si₃N₄ outwardly of the substrate, the outer Si₃N₄ layer having an outer surface;

transforming the outer Si₃N₄ surface into a material effective to promote adhesion of photoresist to the Si₃N₄ layer; and

depositing a layer of photoresist over the transformed outer Si₃N₄ surface, the photoresist adhering to the Si₃N₄ layer with a greater degree of adhesion than would otherwise occur if the outer Si₃N₄ surface were not transformed.

Referring to FIGS. 1-4, and initially to FIG. 1, a semiconductor wafer fragment in process is indicated generally with reference numeral 10. Such includes a substrate composed of a bulk monocrystalline silicon substrate 12 and an overlying insulating layer 14, such as SiO₂. An example thickness for layer 14 is from 50 Angstroms to 300 Angstroms.

Referring to FIG. 2, an outer layer 16 of Si₃N₄ is provided outwardly of substrate 12/14. Nitride layer 16 includes an outer surface 18. Thickness of layer 16 will depend upon the application. For example where layer 16 is merely functioning as an etch stop in some later process step, its thickness may approximate 100 Angstroms or less. Where layer 16 is being used as a mask for a local oxidation of silicon (LOCOS), layer 16 thickness may be from 1500 Angstroms to 3000 Angstroms.

The preferred manner of depositing or otherwise providing nitride layer 16 is by chemical vapor deposition within a chemical vapor deposition reactor using a gaseous silicon containing precursor and a gaseous nitrogen containing precursor. Art example preferred nitride precursor is dichlorosilane (DCS), with a preferred nitrogen containing precursor being ammonia (NH₃). One example set of deposition parameters includes maintaining reactor temperature and pressure at 780° C. and 250 mTorr, respectively, with the precursors being provided at a volumetric ratio of DCS:NH₃ at 1:3. Such is but one example set of conditions effective to deposit a Si₃N₄ layer on substrate 14/12.

Referring to FIG. 3, the gas flow of the nitrogen containing precursor to the chemical vapor deposition reactor is reduced, thus increasing the concentration of the silicon component of the precursor. This will have the effect of enrichening the Si₃N₄ layer outermost surface 18 to outermost surface 18 a with silicon atoms, as depicted by the dots in the FIG. 3, to provide increased silicon concentration beyond the empirical stoichiometric relationship of silicon to nitride atoms in molecular silicon nitride. Thus, the outer silicon nitride surface has been transformed into a material (i.e. silicon enrichened Si₃N₄) which can effectively be used to promote subsequent adhesion of photoresist to Si₃N₄ layer 16 a. Silicon is a material to which photoresist will more readily adhere than Si₃N₄. An example reduction from the 1:3 DCS:NH₃ ratio to achieve such enrichening is to a ratio of from 1:0 to 1:1.25.

Referring to FIG. 4, a layer of photoresist is deposited over silicon enrichened outer Si₃N₄ surface 18 a, and is for example patterned as shown to produce photoresist blocks 20. Silicon enrichened outer surface 18 a can optionally be treated with suitable other adhesion primers appropriate to silicon, such as HMDS. Regardless, a desired result is photoresist material 20 adhering to Si₃N₄ layer 16 a with a greater degree of adhesion than would otherwise occur if the outer Si₃N₄ surface 18 were not transformed by silicon enrichening. All of the above described processing preferably and advantageously occurs in the same single chemical vapor deposition reactor. Alternately, more than one reactor chamber can be used.

An alternate embodiment 22 is described with reference to FIGS. 5 and 6. Such comprises a substrate composed of bulk monocrystalline silicon 24 and an overlying SiO₂ layer 26. An outer predominantly nitride layer 28 is provided over SiO₂ layer 26. Such also includes an outer surface 30, the immediately underlying portion thereof which has been transformed to an oxidized material 32, preferably SiO₂. Bulk mass 34 of layer 28 constitutes Si₃N₄. The processing to produce materials 34 and 32 preferably is again conducted in a single, common chemical vapor deposition reactor.

Material 32 relative to outer surface 30 is preferably provided by feeding a gaseous oxygen containing precursor to the reactor under conditions effective to oxidize Si₃N₄ material 34 to SiO₂ material 32. One example process for accomplishing such transformation of outer surface 30 is to cease feeding the dichlorosilane and ammonia precursors as described in the above example, and purging the reactor of such gaseous precursors. Immediately thereafter, N₂O, O₂, O₃, or mixtures thereof are fed to the reactor under the same temperature and pressure conditions which effectively causes the outer surface of the nitride material to become oxidized to SiO₂. The thickness of material 32 is preferably kept very low, such as from about 10 Angstroms to about 30 Angstroms. Purging of the Si₃N₄ precursors is highly desirable to prevent an undesired silicon dust from falling out onto the wafer as may occur without purging, which neither produces the SiO₂ material of this example, nor readily adheres to the underlying substrate.

An example processing for O₃, would be at atmospheric or subatmospheric pressure at a temperature of 600° C. for from one to two hours. For O₂, an example oxidizing condition would be feeding both O₂ and H₂ at atmospheric pressure and temperatures ranging from 800° C. to 1100° C. for from 30 minutes to two hours.

Alternately but less preferred, the above processing could take place in two separate chambers, with the wafer(s) being moved from one to the other after provision of the nitride layer for subsequent provision of the adhesion promoting layer.

Referring to FIG. 6, a layer of photoresist is deposited and patterned to produce photoresist blocks 36, as in the first described embodiment. The photoresist adheres to Si₃N₄ layer 28 with a greater degree of adhesion than would otherwise occur if the outer Si₃N₄ surface 30 were not oxidized.

Other alternate examples are described with reference to FIG. 7, illustrating a semiconductor wafer fragment 40. Such again comprises a substrate composed of a bulk monocrystalline silicon substrate 42 and overlying SiO₂ layer 44. An overlying layer 46 of Si₃N₄ is provided, preferably as described above with respect to the other embodiments. Nitride layer 46 has an outer surface 48. Subsequently, conditions are provided within a chemical vapor deposition reactor to cover outer Si₃N₄ surface 48 with a discrete photoresist adhesion layer 50 having a thickness of preferably from about 10 Angstroms to about 30 Angstroms. Thus, an outer composite substrate layer 52 is provided which predominantly comprises Si₃N₄. Example and preferred materials for thin discrete photoresist adhesion layer 50 are silicon or SiO₂.

Silicon can be deposited by any typical or known process for depositing polycrystalline silicon atop a semiconductor wafer. An example and preferred method for providing layer 50 to constitute SiO₂ is to first purge the reactor after Si₃N₄ later deposition, followed by feeding of DCS and N₂O to the reactor under temperature conditions of 780° C. and 250 mTorr at a volumetric ratio of DCS:N₂O of from 1:3 to 1:10. Subsequently provided photoresist will adhere to Si₃N₄ layer 52 with a greater degree of adhesion than would otherwise occur if the intermediate silicon, SiO₂, or other adhesion promoting layer were not present.

In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents. 

What is claimed is:
 1. A semiconductor processing method comprising: providing a substrate; forming a layer over the substrate; the layer comprising a lower portion and an upper portion over and against the lower portion; the lower portion comprising a first concentration of silicon and a second concentration of nitrogen, the ratio of the second concentration to the first concentration being a first ratio; the upper portion comprising a third concentration of silicon and a fourth concentration of nitrogen, the ratio of the fourth concentration to the third concentration being a second ratio; the second ratio being less than the first ratio; and forming a layer of photoresist in physical contact with the upper portion.
 2. The method of claim 1 wherein the second ratio is greater than
 0. 3. A semiconductor processing method comprising: providing a substrate; forming a first layer of silicon nitride over the substrate, the layer of silicon nitride having a first outer surface; forming a second layer of silicon nitride over and in contact with the first outer surface, the second layer forming a second outer surface enriched with respect to the first outer surface in silicon; and after forming the enriched second outer surface, forming a layer of photoresist in physical contact with the second outer surface.
 4. A semiconductor processing method comprising: providing a monocrystalline silicon substrate; placing the substrate within a chemical vapor deposition reactor; feeding a gaseous silicon containing precursor and a gaseous nitrogen containing precursor to the reactor under conditions effective to deposit a first Si₃N₄ layer on the substrate; reducing the gas flow of the nitrogen containing precursor to the reactor to form a second Si₃N₄ layer over the first Si₃N₄ layer, the second Si₃N₄ layer having an outermost surface of the deposited Si₃N₄ layer enriched with silicon atoms as compared to the first Si₃N₄ layer; and depositing a layer of photoresist in physical Contact with the silicon enriched outer Si₃N₄ surface.
 5. The semiconductor processing method of claim 4 wherein the silicon containing precursor comprises dichlorosilane and the nitrogen containing precursor comprises ammonia.
 6. The semiconductor processing method of claim 4, wherein forming the first Si₃N₄ layer and forming the second Si₃N₄ layer are performed in a single continuous process.
 7. The semiconductor processing method of claim 3, wherein forming the first layer and forming the second layer are performed in a single continuous process. 